Magnetic memory

ABSTRACT

A magnetic memory includes: a magnetoresistance effect element having a magnetic recording layer; a first writing wiring extending in a first direction on or below the magnetoresistance effect element, a center of gravity of an axial cross section of the wiring being apart from a center of thickness at the center of gravity, and the center of gravity being eccentric toward the magnetoresistance effect element; and a writing circuit configured to pass a current through the first writing wiring in order to record an information in the magnetic recording layer by a magnetic field generated by the current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/345,188, filed Jan. 16, 2003, now U.S. Pat. No. 6,831,855 and isbased upon and claims the benefit of priority from the prior JapanesePatent Application No. 2002-007878, filed on Jan. 16, 2002; the entirecontents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic memory, and more particularly, to amagnetic memory which can reduce power consumption by applying amagnetic field to a record layer of the magnetoresistance effect elementefficiently by small write-in current.

Recently, there is a proposal of magnetic random access memory using amagnetic element exhibiting giant magnetoresistance effect as a solidmagnetic storage device. Especially, magnetic memory using“ferromagnetic tunnel junction” is remarked as a magnetic element.

Ferromagnetic tunnel junction is mainly made of a three-layered film offirst ferromagnetic layer/insulating film/second ferromagnetic layer,and a current flows, tunneling through the insulating film. In thiscase, the junction resistance value varies proportionally to the cosineof the relative angle between magnetization directions of the first andsecond ferromagnetic layers. Therefore, resistance value becomes minimumwhen the magnetization directions of the first and second ferromagneticlayers are parallel, and becomes maximum when they are anti-parallel.This is called tunneling magnetic resistance (TMR) effect. For example,in the literature, Appl. Phys. Lett., Vol. 77, p 283(2000), it isreported that changes of resistance value by TMR effect reaches as highas 49.7% at the room temperature.

In a magnetic memory including a ferromagnetic tunnel junction as amemory cell, magnetization of one of ferromagnetic layers is fixed as a“reference layer”, and the other ferromagnetic layer is used as a“recording layer”. In this cell, by assigning parallel and anti-parallelmagnetic orientations of the reference layer and the recording layer tobinary information “0” and “1”, information can be stored.

For writing information, magnetization of the recording layer isreversed by a magnetic field generated by supplying a current to a writeline provided for the cell. In many cases, magnetization reversal isperformed by passing write-in current simultaneously to two write-inwirings which cross each other without touching, and thereby applying asynthetic magnetic field in the direction which has a certain anglewhich is not zero to a magnetization easy axis of a memory layer.

Moreover, in the case of this write-in operation, an “asteroid curve”indicating the relation between the direction of an applied magneticfield and a reversal magnetic field is taken into consideration.

On the other hand, read out is performed by flowing a sense currentthrough the ferromagnetic tunnel junction, and by detecting a resistancechange by TMR effect. A number of such memory elements are aligned toform a large-capacity memory device.

Its actual configuration is made up by placing a switching transistorfor each cell and combining peripheral circuits similarly to DRAM(dynamic random access memory), for example. There is also a proposal ofa system incorporating ferromagnetic tunnel junctions in combinationwith diodes at crossing positions of word lines and bit lines (U.S. Pat.Nos. 5,640,343 and 5,650,958).

For higher integration of magnetic memory elements using ferromagnetictunnel junctions as memory cells, the size of each memory cell becomessmaller, and the size of the ferromagnetic element forming the cellinevitably becomes smaller. There is the same situation in magneticrecording systems when the recording density is enhanced and therecording bit size is decreased.

In general, as the ferromagnetic element becomes smaller, its coerciveforce increases. Since the intensity of the coercive force givescriteria for judging the magnitude of the switching magnetic fieldrequired for reversal of magnetization, its increase directly means anincrease of the switching magnetic field. Therefore, upon writing bitinformation, a larger current must be supplied to the write line, and itinvites undesirable results such as an increase of power consumption,shortening the wiring lifetime, etc. Therefore, it is an important issuefor practical application of high-integrated magnetic memory to reducethe coercive force of the ferromagnetic element used as the memory cellof magnetic memory.

In order to solve this problem, a magnetic memory element equipped witha thin film which becomes the circumference of write-in wiring frommaterial which has a high magnetic permeability is proposed (the U.S.Pat. No. 5,659,499, the U.S. Pat. No. 5,956,267, the U.S. Pat. No.5,940,319, and international patent application WO 00/10172).

In these elements, a magnetic flux generated by write-in current can beconverged by thin film which has a high magnetic permeability in thecircumference of write-in wiring. Therefore, a magnetic field generatedat the time of writing can be strengthened, and bit information can bewritten in with smaller current as the result. At the same time, since amagnetic flux which leaks to the exterior of a highmagnetic-permeability thin film can be reduced greatly, an effect whichcan reduce cross talk is also acquired.

However, in the case of the structure currently disclosed in the U.S.Pat. No. 5,659,499, a magnetic field cannot be uniformly applied overthe magnetic whole record layer.

Moreover, in the case of the structure disclosed in the U.S. Pat. No.5,956,267 and the U.S. Pat. No. 5,940,319, a magnetic field cannot beapplied efficiently to the magnetic record layer, since a distancebetween the high magnetic-permeability thin film and the magnetic recordlayer is large and especially the distance becomes too large in the casewhere two or more magnetization pinned layers are provided in order toobtain a higher output.

On the other hand, in the case of structure disclosed in theinternational patent application WO 00/10172, it has structure wheredistance between the high magnetic-permeability thin film and themagnetic record layer becomes small, however, it is difficult toconcentrate sufficient magnetic flux to the magnetic record layer.

Moreover, in any of these disclosures, it is not devised at all about across sectional shape of the write-in wiring.

SUMMARY OF THE INVENTION

This invention is made based on recognition of this subject, and byapplying a magnetic field to a magnetic record layer efficiently bywrite-in smaller current, the purpose is the degree of highaccumulation, and is to reduce power consumption and offer a reliablemagnetic memory element.

According to an embodiment of the invention, there is provided amagnetic memory comprising:

a magnetoresistance effect element having a magnetic recording layer;

a first writing wiring extending in a first direction on or below themagnetoresistance effect element, a center of gravity of an axial crosssection of the wiring being apart from a center of thickness at thecenter of gravity, and the center of gravity being eccentric toward themagnetoresistance effect element; and

a writing circuit configured to pass a current through the first writingwiring in order to record an information in the magnetic recording layerby a magnetic field generated by the current.

According to another embodiment of the invention, there is provided amagnetic memory comprising:

a magnetoresistance effect element having a magnetic recording layer;

a first writing wiring extending in a first direction on or below themagnetoresistance effect element, an axial cross section of the wiringbeing formed into a shape which is asymmetric in a vertical directionand a width of the shape being broader toward the magnetoresistanceeffect element; and

a writing circuit configured to pass a current through the first writingwiring in order to record an information in the magnetic recording layerby a magnetic field generated by the current.

According to yet another embodiment of the invention, there is provideda magnetic memory comprising:

a magnetoresistance effect element having a magnetic recording layer;

a first writing wiring extending in a first direction below themagnetoresistance effect element, a center of gravity of an axial crosssection of the first writing wiring being apart from a center ofthickness at the center of gravity, and the center of gravity beingeccentric toward the magnetoresistance effect element;

a second writing wiring extending in a second direction to intersect thefirst direction on the magnetoresistance effect element, a center ofgravity of an axial cross section of the second writing wiring beingapart from a center of thickness at the center of gravity, and thecenter of gravity being eccentric toward the magnetoresistance effectelement; and

a writing circuit configured to pass currents through the first andsecond writing wirings in order to record an information in the magneticrecording layer by magnetic fields generated by the currents.

According to yet another embodiment of the invention, there is provideda magnetic memory comprising:

a magnetoresistance effect element having a magnetic recording layer;

a first writing wiring extending in a first direction below themagnetoresistance effect element, an axial cross section of the firstwriting wiring being formed into a shape which is asymmetric in avertical direction and a width of the shape being broader toward themagnetoresistance effect element;

a second writing wiring extending in a second direction to intersect thefirst direction on the magnetoresistance effect element, an axial crosssection of the second writing wiring being formed into a shape which isasymmetric in a vertical direction and a width of the shape beingbroader toward the magnetoresistance effect element; and

a writing circuit configured to pass currents through the first andsecond writing wirings in order to record an information in the magneticrecording layer by magnetic fields generated by the currents.

According to yet another embodiment of the invention, there is provideda magnetic memory comprising:

a magnetoresistance effect element having a magnetic recording layer;

a first writing wiring extending in a first direction below themagnetoresistance effect element,

a second writing wiring extending in a second direction to intersect thefirst direction on the magnetoresistance effect element,; and

a writing circuit configured to pass currents through the first andsecond writing wirings in order to record an information in the magneticrecording layer by magnetic fields generated by the currents,

a shape of an axial cross section of the first writing wiring beingdifferent from a shape of an axial cross section of the second writingwiring,

the shapes of the axial cross sections of the first and second writingwirings are rectangular or trapezoidal,

one of the first and second writing wirings being remoter from themagnetoresistance effect element, and

and the remoter wiring having a larger ratio of a length of one sidewhich is closer to the magnetoresistance element to a length of anotherside which is remoter from the magnetoresistance effect element thananother of the first and second writing wirings.

As explained in full detail above, according to the embodiment, amagnetic field can be efficiently applied to the magnetic record layerof the magnetoresistance effect element by giving form peculiar to theaxial cross section of the wiring for writing of a magnetic memory.

Write-in current required as the result, in order to record bitinformation can be reduced greatly, and a magnetic memory with littlepower consumption can be offered.

Thus, according to the embodiment, the magnetic memory of the degree ofhigh integration can be realized with low power consumption, and themerit on industry is great.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of theembodiments of the invention. However, the drawings are not intended toimply limitation of the invention to a specific embodiment, but are forexplanation and understanding only.

In the drawings:

FIG. 1A is a conceptual diagram showing a principal part of the crosssectional structure of a magnetic memory according to an embodiment ofthe invention;

FIG. 1B shows the A–A′ line sectional view;

FIGS. 2A and 2B are conceptual diagrams showing the memory cell of themagnetic memory as an example of comparison;

FIGS. 3A through 3D are schematic cross sectional diagrams showing theprocess of the fabrication method of wirings 22 and 23;

FIGS. 4A through 5B are conceptual diagrams which show the examples ofthe embodiment;

FIGS. 6A through 6D are schematic diagrams showing a process tofabricate a wiring having a trapezoid cross section;

FIGS. 7A through 7D are schematic diagrams showing a process tofabricate a wiring having a circular cross section;

FIGS. 8A and 8B are conceptual diagrams showing another example of theembodiment;

FIGS. 9A through 10B are conceptual diagrams showing the furtherexamples of the embodiment;

FIG. 11 is a conceptual diagram which exemplifies the matrix structureof the magnetic memory of the embodiment;

FIG. 12 is a conceptual diagram showing another example of the matrixstructure of the magnetic memory of the embodiment;

FIG. 13 is a graphical representation showing the magnetic fielddistribution where the width and thickness of the wiring are changedwhile setting a cross section area constant;

FIG. 14 is a graphical representation which plotted the generatingmagnetic field, respectively about the cases where the cross sectionalshapes of wiring are a rectangle and a trapezoid;

FIG. 15 is a schematic diagram showing the cross section of the write-inwiring 23;

FIG. 16 is a graphical representation showing the intensity of thecurrent magnetic field at the distance Z from wiring 23;

FIG. 17 is a graphical representation by which the relation of thecurrent magnetic field to W2/W1 is plotted;

FIG. 18A is a schematic diagram which shows the magnetic memory wherethe cross sectional shapes of upper and lower wirings differ each other;

FIG. 18B is the A–A′ line sectional view;

FIGS. 19A and 19B are schematic diagrams showing the case where thelower wiring 23 separates from the magnetoresistance effect element 21further;

FIGS. 20A and 20B are schematic diagrams showing the cell structure ofthe magnetic memory of the example; and

FIG. 21 is a graphical representation which shows the distribution ofthe generating magnetic field when passing 2 mA write-in current to suchwiring 22.

DETAILED DESCRIPTION

Some embodiments of the invention will now be explained below withreference to the drawings.

FIG. 1A is a conceptual diagram showing a principal part of the crosssectional structure of a magnetic memory according to an embodiment ofthe invention.

And FIG. 1B shows the A–A′ line sectional view.

That is, the structure shown in these figures corresponds to the memorycell of the 1-bit portion of the magnetic memory which operates as arandom access memory.

This memory cell consists of a storage cell portion 11 and a transistorportion 12 for address selection. The storage cell portion 11 has themagnetoresistance effect element 21 and a pair of wiring 22 and 24connected to the element 21. The magnetoresistance effect element 21 hasthe laminating structure of for example, a magnetic layer/non-magneticlayer/magnetic layer, or a magnetic layer/insulated tunnellayer/magnetic layer, and may have the GMR effect, the TMR effect, etc.

What is necessary is to pass sense current for the magnetoresistanceeffect element 21 in the case of bit information read-out, and just todetect the resistance change, in the case where the element 21 has theGMR effect.

If the element 21 has a ferromagnetic double tunnel junction structuresuch as magnetic layer/non-magnetic tunnel layer/magneticlayer/non-magnetic tunnel layer/magnetic layer etc., it is advantageousat a point that the high magnetoresistance effect is acquired by a largeresistance change by the tunnel magnetoresistance (TMR) effect.

In such structures, one of magnetic layers shall act as a magnetizationpinned layer, and one of other magnetic layers shall act as a magneticrecord layer.

As for a magnetization pinned layer and a magnetic record layer, it isdesirable to include a ferromagnetic substance layer which consists ofan alloy containing iron (Fe), cobalt (Co), nickel (nickel), or one ofthese etc., or to include half-metallic magnetic layers, such as nickelmanganese antimony (NiMnSb), platinum manganese antimony (PtMnSb), andcobalt manganese germanium (Co₂MnGe).

As for the magnetization pinned layer, the thickness of these magneticlayers may be increased in order to obtain a higher coercive force.

Or magnetization can be pinned by exchange interaction which worksbetween a magnetic layer and an anti-ferromagnetic layer by employing astructure where the laminating of the anti-ferromagnetic layer wascarried out to a magnetization pinned layer.

On the other hand, a transistor 30 connected through a via 26 and buriedwiring 28 is formed in a transistor portion 12 for selection. Thistransistor 30 carries out switching operation according to the voltageapplied to a gate 32, and controls switching of the current path betweenthe magnetoresistance effect element 21 and wiring 34.

Moreover, under the magnetoresistance effect element, the write-inwiring 23 is formed in the direction which intersects the wiring 22.These write-in wirings 22 and 23 can be formed with the alloy containingaluminum (aluminum), copper (Cu), tungsten (W), tantalum (Ta), or one ofthese.

In a memory cell of such structure, when writing bit information in themagnetoresistance effect element 21, a write-in pulse current is passedto the wirings 22 and 23. Then, a synthetic magnetic field induced bythese current is applied to a record layer, and magnetization of arecord layer of the magnetoresistance effect element can be reversedsuitably.

On the other hand, when reading bit information, sense current is passedthrough wiring 22, the magnetoresistance element 21 containing amagnetic-recording layer, and the lower electrode 24, and a change ofthe resistance of the magnetoresistance effect element 21 or resistanceitself is measured.

In this embodiment, the axial cross sectional shape of wiring 22 and 23is asymmetrical in the vertical direction. And when taken along with thecentral line of the magnetoresistance effect element 21, the center ofgravity of the cross section of these wiring is in the position offsetfrom the center of the thickness direction of the wiring toward themagnetoresistance effect element 21.

For example, with reference to FIG. 1B, when taken along with thecentral line L of the magnetoresistance effect element 21, the center ofgravity G of the axial cross section is in the position is off-centeredtowards the magnetoresistance effect element 21 from the central point Cin the thickness direction of wiring 22.

In order to make the eccentricity of the center of gravity G in thedirection of the magnetoresistance effect element 21, what is necessaryis just to give the cross section where the width of the section of thewrite-in wiring 22 and 23 becomes broader towards the magnetoresistanceeffect element 21, for example, as shown in FIG. 1B.

FIGS. 2A and 2B are conceptual diagrams showing the memory cell of themagnetic memory as an example of comparison. With regard to FIGS. 2A and2B, the same symbol is given to the similar element as what wasmentioned above with regard to FIGS. 1A and 1B, and detailed explanationis omitted.

In the case of this example of comparison, the axial cross section ofwirings 22 and 23 has the shape of a substantially rectangle symmetricalin a vertical direction. And the center of gravity G of the crosssection of the wirings is in the same position as the center C of thethickness direction taken along with the central line L of themagnetoresistance effect element 21.

Now, the strength of the magnetic field generated when current is passedto the wirings 22 and 23 having a cross section as shown in FIGS. 1A and1B or 2A and 2B is obtained by the Biot-Savart law. According to thelaw, supposing current density is fixed on each point in a wiringsection, the magnetic field generated in the point X which only acertain distance separated from wiring will be described bysuperposition of the magnetic field generated with the current densityof each point in the section of the wiring.

Since the magnetic field generated with the current density of eachpoint in the section of wiring is in inverse proportion to the distancefrom the point to Point X, a generating magnetic field becomes larger asthe distance becomes smaller.

On the other hand, it is difficult to arrange the wiring and themagnetic record layer closer than a certain distance because of thestructural problem of an actual memory cell. Therefore, it is moreadvantageous to form the cross section of write-in wiring asymmetricallyas shown in FIGS. 1A and 1B rather than symmetrical in a verticaldirection. And by setting the position of center of gravity of the crosssection of write-in wiring eccentric toward the magnetoresistance effectelement rather than the central point in the thickness direction, themagnetic field applied to the magnetoresistance effect element fromwrite-in wiring will becomes stronger.

Therefore, the cross sectional shape of write-in wiring is formed asshown in FIGS. 1A and 1B, the magnetic field applied to themagnetoresistance effect element 21 from the write-in wirings 22 and 23becomes strong, and a magnetic field can be efficiently applied to amagnetic-recording layer.

This point will be explained more quantitatively, referring to someexamples.

According to the embodiment, the power consumption of a magnetic memorycan be reduced by giving the feature peculiar to the cross sectionalshape of write-in wiring in this way.

Moreover, the stable writing is attained, even if the magnetoresistanceeffect element 21 is miniaturized to increase the degree of integrationof magnetic memory and thereby increasing the coercive force of therecording layer.

Furthermore, by reducing the write-in current passed to the write-inwirings 22 and 23, the electro-migration in the wirings can be reduced,the reliability of magnetic memory can be improved, and a life can alsobe prolonged.

Next, the fabrication method of the asymmetrical wirings 22 and 23 whichhas the cross section as shown in FIGS. 1A and 1B is explained.

FIGS. 3A through 3D are schematic cross sectional diagrams showing theprocess of the fabrication method of wirings 22 and 23. That is, first,as shown in FIG. 3A, the magnetoresistance effect element 21 is formedon the lower wiring 24, then the insulating layer 100 is formed at thecircumference of the element 21. Next, as shown in FIG. 3B, the surfaceis polished and a distribution that the thickness of the insulatinglayer 100 becomes gradually thinner in the circumference of themagnetoresistance effect element 21 is provided.

Such an etching distribution can be realized by choosing an appropriateetchant or by adjusting a buff pressure, etc. in chemical mechanicalpolishing, for example. After that, as shown in FIG. 3C, the material ofwiring 22 is deposited on the surface.

Then, the wiring having the shape as shown in FIG. 3D is acquired bycarrying out a patterning process. On this occasion, first, a verticalpatterning is performed by an anisotropic etching process, then thecorners of the wiring 22 are rounded by a wet etching or an isotropicgaseous phase etching.

Alternatively, after preparing a mask which is not illustrated,pattering process may be performed by using a wet etching or anisotropic gaseous phase etching from the beginning in order to fabricatethe rounded wiring 22 as shown in FIG. 3D. The peculiar cross sectionshape shown in FIGS. 1A and 1B can be realized with the process whichwas explained above.

It is not necessary to give such a peculiar asymmetrical cross sectionas shown in FIGS. 1A and 1B for the wirings which does not pass write-incurrent. For example, since the lower wiring 24 is used only forread-out in the case of the example of FIGS. 1A and 1B, it is also goodto employ a usual symmetrical cross section without giving theasymmetrical cross section like wiring 22 and 23. Thus, the formationprocess of wiring 24 becomes simplified.

Next, the example of transformation of the embodiment is explained.

FIGS. 4A through 5B are conceptual diagrams which show the examples ofthe embodiment. The same symbol is given to the similar element as whatwas mentioned above about FIGS. 1A and 1B with regard to these drawings,and detailed explanation is omitted.

In the case of the memory cell shown in FIGS. 4A and 4B, cross sectionof the write-in wirings 22 and 23 is made into the shape of a trapezoidwhere the longer side is closer to the magnetoresistance effect element21. Here, instead of the trapezoidal shape, the axial cross section maybe formed into a substantially triangle. That is, such a triangle can beobtained by making the length of the shorter side of the trapezoidalmost zero. This point will be explained in greater detail later on,with reference to a second example of the invention.

In the case of the memory cell shown in FIGS. 5A and 5B, the crosssection of the write-in wirings 22 and 23 is semicircle-like, and ismade into form from which the arc part is apart from themagnetoresistance effect element 21.

Furthermore, the side S which countered the magnetoresistance effectelement 21 of the cross section of these wirings 22 and 23 is curving tothe concave when taken from the magnetoresistance effect element 21.

Also in the memory cells shown in these FIGS. 4A through 5B, the crosssection of the wirings 22 and 23 is asymmetrical in a verticaldirection, and the center of gravity of the cross section is eccentrictoward the magnetoresistance effect element 21 taken along the centralline of the magnetoresistance effect element 21.

By forming the write-in wirings 22 and 23 which have such peculiarsection form, the magnetic field applied to the magnetoresistance effectelement 21 becomes stronger, and a magnetic field can be efficientlyapplied to a magnetic record layer.

A method to fabricate the shape of a trapezoid and reverse trapezoidcross sections as shown in FIGS. 4A and 4B will be explained next.

FIGS. 6A through 6D are schematic diagrams showing a process tofabricate a wiring having a trapezoid cross section. First, as shown inFIG. 6A, the layer 310 which should be made into the wiring is formed ona base layer 300, and the mask 320 which covers a part is further formedon it.

Next, as shown in FIG. 6B, anisotropic etching A is performed with aninclined incident angle. Specifically, an ion milling or other etchingmethods, such as RIE (Reactive Ion Etching), can be used. Then, theportion on which the masking is not carried out is etched away, and aslope is formed in a boundary with the mask part.

Next, a mask 330 is formed in an opposite side as shown in FIG. 6C.Then, as shown in FIG. 6D, an anisotropic etching B is performed fromthe opposite direction with an inclined incident angle. Then, theportion on which the masking is not carried out is also etched away, anda slope is also formed in the boundary with the mask part. Thus, thewiring having a trapezoid cross section is fabricated by combining theanisotropic etching with a slant etching angle. A wiring which has areverse trapezoid cross section can also be formed by forming an openinghaving a reverse trapezoid cross section by the same process asexplained above, then by burying the object material which forms thewiring in the opening.

Next, a method to fabricate the wiring having the circular cross sectionas shown in FIGS. 5A and 5B will be explained.

FIGS. 7A through 7D are schematic diagrams showing a process tofabricate a wiring having a circular cross section.

First, as shown in FIG. 7A, the layer 410 which should be made into thewiring is formed on a base layer 400, and the mask 420 which covers apart is further formed on it. As this mask, the deformable material isdesirable. For example, a resist or polyimide can be used.

Next, as shown in FIG. 7B, a mask 420 is softened and it roundscircularly with a surface tension. Generally such a softening process ispossible by heating an organic material such as a predetermined resistor others.

Next, as shown in FIG. 7C, anisotropic etching C is given from asubstantially perpendicular direction. As this etching method, an ionmilling and the etching methods, such as RIE (Reactive Ion Etching), canbe used. Then, etching removal of the layer 410 exposed to a mask 420and its circumference is carried out simultaneously, and etchingadvances.

The form of a mask 420 is transferred to the layer 410 as the result.And if etching is advanced further, as shown in FIG. 7D, etching removalof the mask 420 will be carried out completely, and the layer 410 towhich the shape of a mask 420 was transferred will be formed. Thus,wiring having a circular cross section can be fabricated.

Strictly speaking, in the case of this formation process, the crosssectional shape of a mask 420 may differ from the cross sectional shapeof the transferred layer 410 according to a difference of the etchingspeed of a mask 420 and a layer 410. However, it is easy to adjust themask form where the effect of a difference of such an etching selectionratio was taken into consideration, then desired section form can berealized.

FIGS. 8A and 8B are conceptual diagrams showing another example of theembodiment. The same symbol is given to the similar element as what wasmentioned above about FIGS. 1A through 7D with regard to FIGS. 8A and8B, and detailed explanation is omitted.

In this example, the covering layer SM made of a magnetic material andwhich becomes the circumference of the write-in wirings 22 and 23 isadded. That is, the covering layer SM is formed around the wirings 22and 23 so that the surface which does not counter the magnetoresistanceeffect element 21 may be covered. By forming the covering layer SM, theleakage to the circumference of the current magnetic field generatedfrom the write-in wirings 22 and 23 can be prevented, and “the write-incross talk” to the magnetoresistance effect element of other adjoiningmemory cells can be prevented.

Furthermore, when this covering layer SM acts as the so-called “magneticyoke”, as exemplified in FIGS. 8A and 8B, the magnetic field M can beconcentrated to the magnetoresistance effect element 21 and the writingefficiency can be further improved. In order to obtain such a function,as a material of the covering layer SM, it is desirable to use amaterial having a high magnetic-permeability.

It is especially desirable to use a material having a relativepermeability not lower than five, and a material having a relativepermeability not lower 100 is more desirable. Moreover, the one wheresaturation magnetization is larger is desirable, it is desirable that itis 500 or more, and it is more desirable that it is 1000 or more.

As such a material, iron (Fe), an iron aluminum (Fe-aluminum) alloy, aniron silicon (Fe—Si) alloy, and iron silicon aluminum (Fe—Si-aluminum)alloys such as a sendust can be used.

Alternatively, as the material of the covering layer SM, the softferrite which includes a nickel iron (NiFe) alloy or iron oxide (Fe₂O₃)as its main component can be used.

Further, as the material of the covering layer SM, various kinds of highmagnetic-permeability material, such as an amorphous alloy having anyone of iron (Fe), cobalt (Co) and nickel (nickel), and any one of (BoronB), silicon (Si), phosphorous (P) etc., can also be used.

FIGS. 9A through 10B are conceptual diagrams showing the further exampleof the embodiment. That is, in the case of the memory cell shown in FIG.9, cross sectional shape of the write-in wirings 22 and 23 is made to bethe same as that of what was shown in FIGS. 4A and 4B.

Moreover, the similar covering layer SM as what was mentioned above withreference to FIGS. 8A and 8B is formed. By forming such a covering layerSM, as mentioned above about FIG. 8, leakage of the write-in magneticfield to an adjoining memory cell can be prevented, and the generatingmagnetic field to the magnetoresistance effect element 21 can bestrengthened.

Furthermore, in the case of this example, the covering layer SM added tothe circumference of the write-in wiring 22 has the projecting part Pprojected toward the magnetoresistance effect element 21. By formingsuch a projecting part P, it becomes possible to concentrate still moreefficiently the write-in magnetic field emitted from the covering layerSM on the record layer of the magnetoresistance effect element 21.

Moreover, it cannot be overemphasized that the similar projecting part Pmay be formed to the lower write-in wiring 23. Furthermore, in theportion near the magnetoresistance effect element 21, in order tostrengthen a generating magnetic field, the covering layer SM added tothe circumference of wiring 22 and 23 can be formed so that thethickness may become thinner toward a magnetic-recording layer. If itdoes in this way, a write-in magnetic field can be concentrated on arecord layer still more efficiently.

Furthermore, the projecting part P of the covering layer SM can becrooked from the middle of the projecting part taken out from theportion of the origin which adjoined wiring 22, or wiring 22 a total,and it can also be provided so that it may carry out toward themagnetic-recording layer of the magnetoresistance effect element 21. Ifit does in this way, the tip of the projecting part P of the coveringlayer SM can be brought further close to a magnetic-recording layer, andit is possible to concentrate a write-in magnetic field on a recordlayer still more efficiently.

In the case of the memory cell shown in FIG. 10, cross sectional shapeof the write-in wirings 22 and 23 is made to be the same as that of whatwas shown in FIGS. 5A and 5B. Furthermore, the similar covering layer SMas what was mentioned above about FIG. 8A is formed.

Also in this example, by forming such a covering layer SM, leakage ofthe write-in magnetic field to an adjoining memory cell can beprevented, and the generating magnetic field to the magnetoresistanceeffect element 21 can be strengthened. Moreover, also in this example, awrite-in magnetic field can be concentrated on a record layer still moreefficiently by forming the projecting part P which was exemplified inFIGS. 9A and 9B.

Magnetic memory can be formed by arranging a memory cell which wasexplained above in the shape of a matrix.

FIG. 11 is a conceptual diagram which exemplifies the matrix structureof the magnetic memory of the embodiment. That is, this figure shows thecircuit structure of the embodiment in the case of having arranged thememory cell mentioned above with reference to FIGS. 1A through 10B inthe shape of a matrix array.

In order to choose 1 bit in an array, it has the sequence decoder 50 andthe line decoder 51. By selecting the bit line 34 and the word line 32,specific switching transistor 30 is turned on and a specific cell ischosen uniquely. And the bit information recorded on themagnetic-recording layer which constitutes the magnetoresistance effectelement 21 can be read by detecting with a sense amplifier 52.

When writing in bit information, writing current is passed in thespecific write-in word line 23 and the specific bit line 22,respectively, and the current magnetic field is applied to the recordinglayer of a specific cell. In this structure, since the cross sectionalshape of the bit lines 22 and the word lines 23 has peculiar shape asexemplified in any of FIGS. 1A through 7B, writing is performedefficiently to the magnetic-recording layer of the magnetoresistanceeffect element 21.

FIG. 12 is a conceptual diagram showing another example of the matrixstructure of the magnetic memory of the embodiment. That is, in the caseof this example, the bit lines 22 and word lines 34 which were wired inthe shape of a matrix are chosen by decoders 60 and 61, respectively,and the specific memory cell in an array is chosen uniquely.

Each memory cell has the structure where Diode D is connected with themagnetoresistance effect element 21 in series. Here, Diode D has therole to prevent that sense current detours in memory cells other thanmagnetoresistance effect element 21 selected.

In writing, write-in current is passed in a specific bit line 22 and aword line 23, thereby applying the current magnetic field to therecording layer of a specific cell. Also in this matrix structure, sincethe cross sectional shape of the bit lines 22 and word lines 23 haspeculiar shape as exemplified in any of FIGS. 1A through 7B, the writingto the magnetic-recording layer of the magnetoresistance effect element21 can be performed efficiently.

EXAMPLE

Embodiments of the invention will be explained below in greater detailwith reference to Examples. That is, here explains the result of havinginvestigated quantitatively the magnetic field which the wiringgenerates, giving an example about the cross sectional shape of thewrite-in wirings 22 and 23 of the magnetic memory of this invention withsome comparative samples.

First Example

First, as shown in FIGS. 2A and 2B, the case where the cross section ofwirings 22 and 23 is a rectangle-like is explained.

FIG. 13 is a graphical representation showing the magnetic fielddistribution where the width and thickness of the wiring are changedwhile setting a cross section area constant.

Here, cross section areas of wiring 22 and 23 were set to 0.02 μm², andthe material thereof is copper (Cu) and the current passed to wiring is1 mA. The horizontal axis of FIG. 13 corresponds to the ratio (aspectratio) of thickness to the width of wiring, and a vertical axiscorresponds to the intensity of a magnetic field. In this figure, eachcase where the distance Z from wiring is 50 nm, 100 nm, and 150 nm isplotted.

From the result, it turns out that the aspect ratio at which the peak ofa magnetic field is obtained becomes small as the distance Z from thewiring becomes large. And when Distance Z is 150 nm, it turns out thatthe maximum generating magnetic field is obtained for an aspect ratio inthe about 0.5. That is, in the position of a magnetic record layer, whenthe ratio of width and thickness is 2:1, a magnetic field can begenerated most efficiently.

On the other hand, as shown in FIGS. 4A and 4B, the case where the crosssection of wirings 22 and 23 is a trapezoid-like is explained.

FIG. 14 is a graphical representation which plotted the generatingmagnetic field, respectively about the cases where the cross sectionalshapes of wiring are a rectangle and a trapezoid. Here, the material ofwiring is copper (Cu), the cross section area is set to 0.04 μm², andcurrent is set to 1 mA.

Moreover, the ratio of the longer side and shorter side is set to 3:1 inthe case of the trapezoid cross section. Moreover, the cross sectionareas of the compared rectangle and a trapezoid are set to be the same.

From FIG. 14, it turns out that the generating magnetic field of thewiring having a trapezoid cross section is higher if the distance is inthe range up to 200 nm. Especially, when distance is 50 nm or less, asfor a trapezoid-like cross section, the magnetic field of about 1.3times or more in the case of a rectangle cross section is obtained.

Second Example

Next, it explains in more detail about the magnetic field intensity inthe case of making cross sectional shape of wiring into the shape of atrapezoid as the second example of the invention.

FIG. 15 is a schematic diagram showing the cross section of the write-inwiring 23. That is, wiring 23 has a trapezoid section. And the length ofthe shorter side is set to W1, the length of the longer side is set toW2, and height (thickness) is set to T.

The Inventors have investigated the intensity of the magnetic fieldformed by passing current to this wiring 23 as a function of thedistance Z from wiring.

FIG. 16 is a graphical representation showing the intensity of thecurrent magnetic field at the distance Z from wiring 23. That is, thehorizontal axis of this figure shows the distance Z from wiring 23, anda vertical axis shows magnetic field intensity. Here, the cross sectionarea of wiring 23 is set to 0.04 square microns, height (thickness) T isset to 0.4 microns, and the current passed to wiring 23 is set to 1 mA.

In FIG. 16, six different cases are plotted, that is, the ratio of theshorter side W1 and the longer side W2, W1:W2, being 1:1, 1:3, 1:7, 1:9,1:39 and 1:99.

As shown in FIG. 16, stronger magnetic field can be obtained in the caseof trapezoid (W1:W2≠1:1) than in the case of rectangle (W1:W2=1:2).Moreover, as W2 becomes larger compared to W1, the magnetic fieldbecomes stronger.

FIG. 17 is a graphical representation by which the relation of thecurrent magnetic field to W2/W1 is plotted. That is, the horizontal axisof this figure shows the ratios W2/W1 of the longer side W2 and theshorter side W1, and a vertical axis shows a current magnetic field.

In this figure, the cases where the distance Z from wiring 23 are 5,105, 145 and 205 nm are plotted, respectively.

From this figure, it turns out that if W2/W1 becomes large, a currentmagnetic field also becomes large gradually saturates. Therefore, inorder to generate the largest possible magnetic field, what is necessaryis to make the ratio W2/W1 larger. According to this approach, theultimate shape of the cross section of the wiring would be an inversetriangle.

In the magnetic memory of this embodiment, the wirings 22 and 23 forwriting provided in the upper and lower sides of the magnetoresistanceeffect element 21 are used.

Generally, the distances from the magnetoresistance effect element 21 tothese wirings 22 and 23 are not equal. Therefore, when passingcomparable write-in current to these wirings 22 and 23, it is desirableby changing the cross sectional shapes of wirings 22 and 23 according tothe distance to the magnetoresistance effect element 21 in order toapply the equal magnetic fields to the element 21.

FIG. 18A is a schematic diagram which shows the magnetic memory wherethe cross sectional shapes of upper and lower wirings differ each other.

FIG. 18B is the A–A′ line sectional view.

As exemplified on these drawings, the wirings 22 and 23 of the upper andlower sides of the magnetoresistance effect element 21 are not in theequal distances from the magnetoresistance effect element 21 in manycases.

For example, in FIGS. 18A and 18B, the lower wiring 23 is providedremoter from the element 21. In such a case, shape of the cross sectionof the upper wiring 22 can be made into a rectangle, and the crosssection of the lower wiring 23 can be made into a reverse trapezoid.

Or it is desirable to make the cross section of the upper wiring into atrapezoid where the ratio of the longer side to the shorter side, W2/W1,is smaller, and to make the cross section of the lower wiring into areverse trapezoid where the ratio of the longer side to the shorterside, W2/W1, is larger.

If it does in this way, the magnetic field given to themagnetoresistance effect element 21 from the upper and lower wirings 22and 23 can be equalized.

FIGS. 19A and 19B are schematic diagrams showing the case where thelower wiring 23 separates from the magnetoresistance effect element 21further.

In this case, it is possible by making cross sectional shape of wiring23 into the shape of a triangle to obtain an appropriate magnetic fieldintensity at the magnetoresistance effect element 21.

In contrast to the examples shown in FIGS. 18A through 19B, when theupper wiring 22 is further from the magnetoresistance effect element 21,the cross section of the wiring 22 may be a trapezoid where W2/W1 islarger or a triangle.

What is necessary is just to determine the shape of the cross section ofwrite-in wiring in consideration of the distance to themagnetic-recording layer of the magnetoresistance effect element 21. Asexplained above, when the distances to the upper and lower wirings 22and 23 from the magnetoresistance effect element 21 are not equal,equalized current magnetic fields from these wirings 22 and 23 can beobtained at the magnetoresistance effect element 21 by differing theshapes of the cross sections of these wirings 22 and 23 suitably.

Third Example

Next, the example having the covering layer SM is explained as the thirdexample of the invention.

FIGS. 20A and 20B are schematic diagrams showing the cell structure ofthe magnetic memory of this example. The same symbol is given to thesimilar element as what was mentioned above about FIGS. 1A through 19Bwith regard to FIGS. 20A and 20B, and detailed explanation is omitted.

In this case of the operation, cross sectional shape of wiring 22 ismade into the shape of a rectangle with a width of 200 nm and athickness of 100 nm, which consists of copper (Cu), and thecircumference is covered with the nickel iron (NiFe) having a relativepermeability of 1000, and the projecting part P whose amount ofprojection is 100 nm is provided.

FIG. 21 is a graphical representation which shows the distribution ofthe generating magnetic field when passing 2 mA write-in current to suchwiring 22. The figure also shows the comparative case where the coveringlayer SM is not formed.

From this result, it turns out that a generating magnetic field becomesabout 1.7 times larger by surrounding the circumference of wiring by thecovering layer SM which consists of the high magnetic-permeabilitymagnetic substance.

Heretofore, embodiments of the invention have been explained in detailwith reference to some specific examples. The invention, however, is notlimited to these specific examples.

For example, material, shape and thickness of the ferromagnetic layer,anti-ferromagnetic layer, insulating film and ferromagnetic film of themagnetoresistance effect element according to the invention may beappropriately selected by those skilled in the art within the knowntechniques to carry out the invention as taught in the specification andobtain equivalent effects.

Further, also concerning the magnetic memory according to the invention,those skilled in the art will be able to carry out the invention byappropriately selecting a material or a structure within the knowntechniques.

While the present invention has been disclosed in terms of theembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. A magnetic memory comprising: a magnetoresistance effect elementhaving a magnetic recording layer; a writing wiring extending in a firstdirection on or below the magnetoresistance effect element, in an axialcross section of the wiring, a width of a part closer to themagnetoresistance effect element being greater than a width of a partremoter from the magnetoresistance effect element; and a writing circuitconfigured to pass a current through the writing wiring to recordinformation in the magnetic recording layer by a magnetic fieldgenerated by the current.
 2. A magnetic memory according to claim 1,wherein a face of the wiring which counters the magnetoresistance effectelement is curving to a concave when taken from the magnetoresistanceeffect element.
 3. A magnetic memory according to claim 1, wherein aside surface of the wiring has a flat surface.
 4. A magnetic memoryaccording to claim 1, wherein a side surface of the wiring has a curvedsurface.
 5. A magnetic memory according to claim 1, further comprising acovering layer provided on the writing wiring, wherein the coveringlayer is provided on at least one of both sides and a face remoter fromthe magnetoresistance effect element of the writing wiring.
 6. Amagnetic memory according to claim 5, wherein the covering layer has aprojecting part which projects toward the magnetoresistance effectelement from the writing wiring.
 7. A magnetic memory comprising: amagnetoresistance effect element having a magnetic recording layer; awriting wiring extending in a first direction on or below themagnetoresistance effect element, an axial cross section of the wiringhaving a first part closer to the magnetoresistance effect element and asecond part remoter from the magnetoresistance effect element, thesecond part having a width smaller than a width of the first part; and awriting circuit configured to pass a current through the writing wiringto record information in the magnetic recording layer by a magneticfield generated by the current.
 8. A magnetic memory according to claim7, wherein a face of the wiring which counters the magnetoresistanceeffect element is curving to a concave when taken from themagnetoresistance effect element.
 9. A magnetic memory according toclaim 7, wherein a side surface of the wiring has a flat surface.
 10. Amagnetic memory according to claim 7, wherein a side surface of thewiring has a curved surface.
 11. A magnetic memory according to claim 7,further comprising a covering layer provided on the writing wiring,wherein the covering layer is provided on at least one of both sides anda face remoter from the magnetoresistance effect element of the writingwiring.
 12. A magnetic memory according to claim 11, wherein thecovering layer has a projecting part which projects toward themagnetoresistance effect element from the writing wiring.
 13. A magneticmemory comprising: a magnetoresistance effect element having a magneticrecording layer; a first writing wiring extending in a first directionbelow the magnetoresistance effect element, in an axial cross section ofthe first writing wiring, a width of a part closer to themagnetoresistance effect element being greater than a width of a partremoter from the magnetoresistance effect element; a second writingwiring extending in a second direction to intersect the first directionon the magnetoresistance effect element, in an axial cross section ofthe second writing wiring, a width of a part closer to themagnetoresistance effect element being greater than a width of a partremoter from the magnetoresistance effect element; and a writing circuitconfigured to pass currents through the first and second writing wiringsto record information in the magnetic recording layer by magnetic fieldsgenerated by the currents.
 14. A magnetic memory according to claim 13,further comprising a reading wiring extending in a third direction tosupply a sense current to the magnetoresistance effect element, whereinan axial cross section of the reading wiring is formed into a shapewhich is symmetric in a vertical direction.
 15. A magnetic memoryaccording to claim 13, wherein a side surface of at least one of thefirst and second writing wirings has a flat surface.
 16. A magneticmemory according to claim 13, wherein a side surface of at least one ofthe first and second writing wirings has a curved surface.
 17. Amagnetic memory according to claim 13, further comprising a coveringlayer provided on at least one of the first and second writing wirings,wherein the covering layer is formed on at least one of both sides and aface remoter from the magnetoresistance effect element of the wiring.18. A magnetic memory according to claim 17, wherein the covering layerhas a projecting part which projects toward the magnetoresistance effectelement from the writing wiring.
 19. A magnetic memory comprising: amagnetoresistance effect element having a magnetic recording layer; afirst writing wiring extending in a first direction below themagnetoresistance effect element, an axial cross section of the firstwriting wiring having a first part closer to the magnetoresistanceeffect element and a second part remoter from the magnetoresistanceeffect element, the second part having a width smaller than a width ofthe first part; a second writing wiring extending in a second directionto intersect the first direction on the magnetoresistance effectelement, an axial cross section of the second writing wiring having athird part closer to the magnetoresistance effect element and a fourthpart remoter from the magnetoresistance effect element, the fourth parthaving a width smaller than a width of the third part; and a writingcircuit configured to pass currents through the first and second writingwirings to record information in the magnetic recording layer bymagnetic fields generated by the currents.
 20. A magnetic memoryaccording to claim 19, further comprising a reading wiring extending ina third direction to supply a sense current to the magnetoresistanceeffect element, wherein an axial cross section of the reading wiring isformed into a shape which is symmetric in a vertical direction.
 21. Amagnetic memory according to claim 19, wherein a side surface of atleast one of the first and second writing wirings has a flat surface.22. A magnetic memory according to claim 19, wherein a side surface ofat least one of the first and second writing wirings has a curvedsurface.
 23. A magnetic memory according to claim 19, further comprisinga covering layer provided on at least one of the first and secondwriting wirings, wherein the covering layer is formed on at least one ofboth sides and a face remoter from the magnetoresistance effect elementof the wiring.
 24. A magnetic memory according to claim 23, wherein thecovering layer has a projecting part which projects toward themagnetoresistance effect element from the writing wiring on which thecovering layer is provided.